The present invention relates to a scroll type fluid machine which is a kind of a displacement type fluid machine.
In a fixed crank type scroll fluid machine in which an amount of eccentricity is fixed and an orbiting radius of an orbiting scroll is defined, and therefore, a fixed scroll itself or a member for defining a position of the fixed scroll is fixed to a compressor base main body of a chamber. As a method of fixing the fixed scroll at a time of assembling, for example, there is an extremely simple method in which the orbiting scroll is orbited while a crank shaft is rotated at a low speed and screws for fixing are gradually fastened while determining that a position at which contact is the least is an optimum position. In this case, except in an oil free machine, a lubricating oil is poured into a clearance so as to form an oil film, thereby preventing wraps from being excessively brought into contact with each other.
Then, in accordance with this method, since an assembled state is a state that a crank shaft rotates when an assembly is completed, a shift of the fixed scroll from an ideal position is equal to or less than a size of a clearance of side surfaces between both of the wraps (a clearance of a portion where the fixed scroll wrap and the orbiting scroll wrap are close to each other so as to form a seal when placing the orbiting scroll at the orbiting position), so that an average performance level is not reduced.
On the contrary, in a variable crank type in which an amount of eccentricity is variable, described in JP-B2-60-37319, the assembling method mentioned above cannot be employed, and therefore, an assembling jig having a high accuracy or the like is required, so that a high cost is required for manufacturing and processing.
In this case, as a structure in which an orbiting bearing portion is not arranged close to a center of the orbiting wrap and which absorbs a thermal deformation at a time of operation, for example, there is listed up a structure described in JP-A-8-254191.
In the scroll type fluid machine of the fixed crank type, an assembling accuracy is improved in comparison with the variable crank type, and therefore, there is obtained an advantage that an average performance level is improved, however, it is necessary to take the following points into consideration.
In the scroll type fluid machine, a change close to an adiabatic change of expansion and compression of fluid is generated between both of the scrolls, and therefore, temperature level of both of the scrolls at a time of operation is different from the other portions and an amount of thermal expansion becomes different from the other portions. The fixed scroll has a lot of contact portions which are in contact with portions other than the orbiting scroll in comparison with the orbiting scroll, so that a free thermal expansion is prevented at the contact portions. Accordingly, at a time of operation, relatively, only the orbiting scroll varies in size. In the fixed crank type in which the orbiting bearing or the orbiting shaft is arranged close to the center of the wrap, the orbiting bearing or the orbiting shaft is combined with an eccentric portion of the crank shaft and the position of the center portion of the orbiting scroll is defined, and therefore, an amount of deformation due to the thermal expansion is increased from the center portion toward an outer periphery. Both of the scrolls become in an engagement state as shown in FIGS. 7 and 8 due to the thermal expansion.
That is, an amount of reduction is increased as being close to an outer periphery of the wrap, that is, the clearance of side surfaces becomes reduced as being close to the outer periphery, at a clearance between an outer side surface of the orbiting wrap and an inner side surface of the fixed wrap of an X spiral portion in an eccentric side in the case of a compressor in which an orbiting scroll 1 thermally expands relatively due to an increase of temperature (refer to FIG. 7), and at a clearance between an inner side surface of the orbiting wrap and an outer side surface of the fixed wrap of a Y spiral portion in an opposite eccentric side in the case of an expansion machine in which the orbiting scroll 1 thermally contracts relatively due to a reduction of temperature (refer to FIG. 8). As a result, a risk that the wraps are interfered with each other (both of the scroll wraps are mechanically brought into contact with each other) can be considered.
Accordingly, conventionally, in order to avoid this risk of interference, that is, in order to prevent the scroll wraps on an outer peripheral side from being brought into contact with each other at a time of thermal expansion, the clearance between both of the wraps is previously increased. In particular, the amount of eccentricity of the fixed crank shaft is set to be smaller than an amount determined in accordance with a shape of the wrap (an ideal value of the orbiting radius). As a result, at a time of assembling upon which there is no thermal deformation, the clearance between the wrap side surfaces is increased. No consideration has been given to a matter that a positioning error of the fixed scroll at a time of assembling increases, the error being determined on the basis of the magnitude of the clearance. That is, no consideration has been given to a matter that dispersion is generated in an assembling accuracy between the orbiting scroll and the fixed scroll, thereby reducing an average performance level.
An object of the present invention is to provide a scroll type fluid machine in which a performance is improved by improving an assembling accuracy (first object) and reliability is improved by giving strength to wraps (second object).
In order to achieve the first object, in accordance with the present invention, there is provided a scroll type fluid machine comprising:
an orbiting scroll having an end plate and a wrap stood on the end plate and orbiting within a surface perpendicular to an axial direction in a direction that the wrap is stood without rotating on its own axis;
a fixed scroll having an end plate and a wrap stood on the end plate and structured such that a motion within the surface perpendicular to the axial direction is restricted; and
a crank mechanism having a fixed amount of eccentricity, the crank mechanism being provided for orbiting the orbiting scroll, thereby reducing or expanding a volume formed by engaging the wraps of the fixed scroll and the orbiting scroll with each other so as to close between both of the scrolls,
wherein a side surface clearance formed between both of the wraps is formed to be smaller in a range between a central winding start point of the wrap and a section close to a center of the wrap than in a range between the section close to the center of the wrap and a section close to an outer periphery of the wrap, and an orbiting shaft coupled with the orbiting scroll side and the section close to the center of the wrap have an overlapping portion as seen from an axial direction.
More preferably, the section close to the center of the wrap is in a range of 360xc2x0 from the central winding start portion of the wrap.
Only the side surface clearance of the section close to the center of the wrap is narrowed with keeping the clearance of the section close to the outer periphery of the wrap, in which the reduction amount of the side surface clearance between the wraps is large at a time of operation, in a magnitude at a time of assembling. Therefore, it is possible to avoid a risk that the wraps are interfered with each other at a time of operation. A position adjusting operation acting from the orbiting scroll to the fixed scroll or the positioning member of the fixed scroll is generated in the section close to the center, where the side surface clearance between the wraps is made small, at an assembling time during which the fixed scroll or the positioning member of the fixed scroll are gradually fixed by screws while rotating the crank shaft, and therefore, an assembling accuracy can be improved and it is possible to increase an average performance level.
Further, since the section close to the center of the wrap is set to 360xc2x0 from the central winding start portion of the wrap, the portion which can be position adjusting action in each of the side surfaces inside and outside the wrap of the orbiting scroll is limited to one portion within the section close to the center of the wrap, even if the crank shaft is in any rotational phase. Accordingly, the position adjusting action becomes continuously in accordance with the rotation of the crank shaft except the case of moving to the winding start portion of the wrap or the case of moving between the inner curve and the outer curve of the wrap, and therefore, it is possible to prevent an impulsive position adjusting action from being generated and prevent the fixed scroll from generating an unnecessary vibration, whereby an assembling accuracy can be improved.
Further, in order to achieve the second object, in accordance with the present invention, there is provided a scroll type fluid machine comprising:
an orbiting scroll having an end plate and a wrap stood on the end plate and orbiting within a surface perpendicular to an axial direction in a direction that the wrap is stood without rotating on its own axis;
a fixed scroll having an end plate and a wrap stood on the end plate and structured such that a motion within the surface perpendicular to the axial direction is restricted; and
a crank mechanism having a fixed amount of eccentricity, the crank mechanism being provided as drive means for orbiting the orbiting scroll, thereby reducing or expanding a volume formed by engaging the wraps of the fixed scroll and the orbiting scroll with each other so as to close between both of the scrolls,
wherein an orbiting shaft coupled with the orbiting scroll side and a section close to a center of the wrap have an overlapping portion as seen from an axial direction, a side surface clearance formed between both of the wraps is formed to be smaller in a range between a central winding start point of the wrap and the section close to the center of the wrap than in a range between the section close to the center of the wrap and a section close to an outer periphery of the wrap, and a formula Bxe2x88x92A greater than  greater than Cxe2x88x92D is established when setting an average of a wall thickness in the section close to the outer periphery of the wrap (except a winding end portion of the wrap) to A, an average of a wall thickness in the section close to the center of the wrap (except a winding start portion of the wrap) to B, a side surface clearance in the section close to the outer periphery of the wrap to C and a side surface clearance in the section close to the center of the wrap to D.
In accordance with the means mentioned above, it is possible to give a strength to the section close to the center of the wrap where a force is applied via an oil film at a time of operation at a high possibility, thereby improving reliability of both of the wraps.